Terrestrial communications throughout the world has grown to rely heavily on optical fiber communications technology. And there is an increasing flow of signaling information that requires use of multiple optical fibers in communication links from one point to another. The various origination, termination, and relay points for optical fiber distribution systems form huge matrices—much more complicated than, say, a map of the railroads or the electrical power grid infrastructures in the United States and abroad. In fact, some optical fiber links do run along power lines and railroad right-of-ways. But, they also run under seas, across farmers' fields, down city streets, into campuses and within buildings and homes.
Management of complex fiber optic communication systems requires many different types of specialized optical and electronic equipment to ensure that correct signals are continuously being sent and received with minimum interruptions and that any failures are detected and quickly rectified.
At a very basic level, it is necessary to use an optical tap to extract a portion of the optical signal in each fiber within a transmission cable so that its functionality can be monitored. In some cases, monitoring the total optical power level is sufficient [see U.S. patent application Ser. No. 14/203,566 dated Mar. 11, 2014 by G. Miller et al titled MULTI-PURPOSE APPARATUS FOR SWITCHING, AMPLIFYING, REPLICATING, AND MONITORING OPTICAL SIGNALS ON A MULTIPLICITY OF OPTICAL FIBERS]. In other cases where multiple optical channels are simultaneously transmitted on a single fiber using wavelength division multiplexing (WDM), it is often necessary to use arrayed waveguide gratings (AWGs) to separate the individual optical channels before they are directed to monitoring equipment [see U.S. patent application Ser. No. 14/205,368 dated Mar. 12, 2014 by G. Miller et al titled APPARATUS FOR SELECTIVE FIBER OPTICAL CHANNEL MONITORING AND CHANNEL REPLICATION OF WAVELENGTH DIVISION MULTIPLEXED (WDM) SIGNALS]. In other cases, optical splitters and optical switches are also employed for monitoring purposes. Due to the large number of optical fibers used in modern optical communication systems, many optical taps, AWGs, splitters and switches are employed. A multiplicity of these components is typically located inside of an equipment enclosure and these enclosures are mounted in racks that fill equipment bays often with a multiplicity of interconnecting fiber optic patch-cord cables [see U.S. patent application Ser. No. 14/072,528 dated Nov. 5, 2013 by G. Miller et al titled HIGH DENSITY ENCLOSURE FOR OPTICAL MODULES].
Clearly, it is desirable to reduce both the time and expense associated with interconnecting the various pieces of communication equipment within equipment bays and to minimize the optical attenuation associated with these interconnections. And this has been an ongoing evolutionary process for all types of equipment, enclosures and patch-cord cables used in modern fiber optical communication systems.
The state-of-the-art for interconnecting various optical components like optical taps is to pack some manageable number of them into a modular container (also referred to as a cassette) that has optical connectors on one or more of its narrow sides. These modular containers are, in turn, closely packed side-by-side into an equipment enclosure that is mounted in an equipment rack such that most or all of the optical connectors on the modular containers face outward for convenient access.
However, for various reasons, including the desirability of increasing the packing density of the cassettes within an equipment enclosure, the cassettes are sometimes located internal to an equipment enclosure well away from the front panel. [see U.S. patent application Ser. No. 14/072,528 referenced above] In such cases, the connection between an equipment cassette and the front panel of the equipment enclosure is typically made with an optical fiber or multi-fiber optic ribbon cable internal to the equipment enclosure that terminates with an optical connector mounted on the outer surface of the enclosure. Then optical patch-cord cables, also terminated with optical connectors, are used to interconnect equipment enclosures.
While use of optical patch-cord cables in this manner is a broadly used installation practice within equipment bays, it is apparent that in some cases it might be desirable to eliminate one or more optical connectors mounted on the surface of equipment enclosures and simply feed the optical patch-cord cable directly through a hole in the enclosure's surface (panel) so that it may continue to an internal equipment cassette where it can be connected (terminated). This strategy would have several advantages: (1) it would eliminate both the cost and optical attenuation associated with an optical connection located on the surface of the equipment enclosure, (2) the patch-cord could possibly be terminated with an optical connector outside of the equipment enclosure, where access is not limited, and simply passed through a conveniently located hole in the outer surface of the equipment enclosure, (3) this strategy might be used at both ends of the fiber optic patch-cord cable for even greater savings of cost and installation time. However, at present there are no fiber optic cable feedthroughs that are inexpensive, easy to install, and capable of securing a pre-terminated (with optical connector) fiber optic cable patch-cords in place.